The production of polyurethane foams based on alkoxysilane-terminated prepolymers has been described. Thus, for example, in European Patent Publication No. EP 946 629 B1, the entire contents of which are incorporated herein by reference, a foam formulation is described in principle which contains a silane functional prepolymer as a binder. However, such high molecular-weight prepolymers based only on polypropylene oxide are not particularly easy to foam and require for this purpose either special complex application equipment (e.g., FoamMix® from Nordson) or else, as explained in the aforementioned reference, complex formulations with numerous additives, which significantly reduce the viscosity of the system among other things. Although ethylene oxide-containing polyethers are mentioned in the patent specification as possible feedstocks, the particular suitability of these raw materials and details concerning their effective use was not appreciated or described.
European Patent Publication No. EP 1 098 920, the entire contents of which are incorporated herein by reference, describes a similar system based on a distinctly low molecular-weight, silane-terminated polyurethane. However, low molecular-weight, silane-terminated prepolymers of this type contain large quantities of very expensive functional silanes, which also leads to a significantly extended rate of curing (about 24 hours, according to examples 2 and 3 of the reference).
This problem of the low rate of curing was addressed in International Patent Publication No. WO2002/066532, the entire contents of which are incorporated herein by reference, by using alkoxysilane-terminated polyurethanes which were produced with alpha-amino- or alpha-isocyanatosilanes. However, the use of these building blocks, which are particularly reactive owing to their C-1 spacer between silane and functional group, is very complex precisely because of this high reactivity, since premature curing and side reactions have to be avoided, which places high demands on purity and freedom from water of the formulation ingredients and also makes special and expensive additives necessary. Variants of this concept are described in International Patent Publication No. WO2004/092259 and International Patent Publication No. WO2004/104078, the entire contents of each of which are incorporated herein by reference.
In German Patent Publication No. DE 2238741, as well as in International Patent Publication No. WO2004/046218, the entire contents of which are incorporated herein by reference, silane-terminated polymeric isocyanates are described which are suitable for the production of rigid foams. However, the considerable quantity of expensive functional silanes needed, which cause curing to proceed only slowly, is also a disadvantage.